Novice amateur radio power supply

Many of us have accumulated various power supplies from laptops, printers or monitors with a voltage of +12, +19, +22. These are excellent power supplies with protection against short circuit and overheating. Whereas in the home, amateur radio practice, an adjustable, stabilized source is constantly required. If it is not advisable to make changes to the scheme of existing power supply units, then a simple prefix to such a unit will come to the rescue.

It will take

To build an amateur set-top box with continuously adjustable output voltage, we will need:

-;

- mounting box;

- two sockets with an internal diameter of 5.2 mm;

- 10 kΩ potentiometer;

- two fixed resistors 22 kΩ each;

- panel.

Article will consist of several finished parts, each of which will be described in detail step , Features and pitfalls of the components used.

Step-down DC-DC converter on the chip lm2596

chip LM2596, which implemented the module is good,which has overheating protection and short circuit protection, but has several features. Look at the typical version of its inclusion, in this case, the chip edition of the output fixed voltage +5 volts, but for the essence it does not matter:

Maintaining a stable voltage level is provided by connecting the feedback output of the fourth (Feed Back) foot of the chip connected directly to the output of the stabilized voltage. In the specific module under consideration the chip is edited with variable output voltage, but the principle of output voltage regulation is the same:

To the output of the module, a resistive divider R1- R2 is connected with the upper trimming resistor R1 turned on, introducing a resistance, which the output voltage of the microcircuit can be changed. In this module, R1 = 10 kΩ R2 = 0.3 kΩ. The bad thing is that the adjustment is not smooth and is carried out only at the last 5-6 turns of the trimming resistor. To implement a smooth adjustment of the output voltage, hams eliminate the R2 resistor, and the trimming resistor R1 is changed to variable.The scheme goes like this:

And just here, there is already a serious problem. The fact is, during the operation of the variable resistor, sooner or later, the contact (its fit to the resistive horseshoe) of the average output is broken and the output 4 (Feed Back) of the microcircuit turns out (even for a millisecond) in the air. This leads to instantaneous failure of the microcircuit. The situation is just as bad when conductors are used to connect a variable resistor - the resistor is external, this can also contribute to the loss of contact. Therefore, the regular resistive divider R1 and R2 should be evaporated, and instead of it, solder two constants directly on the board - this solves the problem of losing contact with the variable resistor in any cases. The variable resistor itself should be soldered to the outputs of the soldered ones. On the diagram, R1 = 22kΩ and R2 = 22kΩ, and R3 = 10kΩ. On the real scheme. R2 was resistance to its labeling, but R1 surprised me, although 10 kOhm was actually marked on it,its nominal resistance turned out to be 2 kΩ.

Remove R2 and put a drop of solder in its place. Remove the resistor R1 and turn the board on the opposite side:

Solder two new R1 and R2 resistors using a photo. As you can see, the future conductors of the variable resistor R3 will be connected to the three points of the divider. Everything, we will set the module aside. Next panel panel power meter.

A DSN-VC288 voltmeter

DSN-VC288 is not suitable for assembling a laboratory power supply, since the minimum current that can be measured using it is 10 mA . But the ampere-voltmeter is great for assembling an amateur construction, and therefore, I will use it. The view from the back is:

Pay attention to the location of the connectors and the available adjustment elements and especially to the height of the current measurement connector:

>img src="https://sdelaysam-svoimirukami.ru/uploads/posts/2018-09/medium/1536559267_201.jpg" style="max-width: 100%;" alt="The power supply of the beginner radio amateur">

Since the case I have chosen for this homemade product does not have sufficient height,then the metal pins of the current connector DSN-VC288 I had to eat, and the attached thick conductors - solder on the pins themselves. Before soldering, make a loop at the ends of the wiring, and solder each one onto each pin for reliability:

Scheme

Schematic diagram of the connection DSN-VC288 and lm2596

Left side DSN-VC288:

- the black thin wire does not connect to anything, insulate it end;

- connect the yellow thin to the positive output of the module lm2596 - PLUS LOAD;

- connect the red thin to the positive input of the module lm2596.

The right side of the DSN-VC288:

- connect the thick black to the negative output of the module lm2596;

- red thick will MINUS LOAD.

Final assembly of the block

I used the mounting box with dimensions of 85 x 58 x 33 mm: By drawing the markup with a pencil, a Dremel disk, I cut out the window for the DSN-VC288 to fit the internal rim of the device. At the same time, at first I sawed through the diagonals, and then, sawed off some sectors along the perimeter of the marked rectangle.A flat file will have to work, gradually adjusting the window under the inner side of DSN-VC288:

In these photos, the cover is not transparent. I decided to use the transparent later, but it doesn’t matter, except for transparency, they are absolutely the same. Also, mark the hole for the threaded collar of the variable resistor:

Please note that the mounting ears of the base half of the box are cut off. And on the microcircuit itself, it makes sense to stick a small radiator. I was ready to hand, but it is not difficult to cut a similar one out of a radiator, say, an old video card. I cut out a similar one for installation on a PCH laptop chip, nothing complicated =)

The mounting ears would prevent the installation of such 5.2mm sockets:

As a result, you should get exactly this: At the same time, on the left is the input jack,right - exit:

Test

Power up the console and look at the display. Depending on the position of the axis of the variable resistor, the device can show different volts, but the current should be zeros. If this is not the case, then the instrument will need to be calibrated. Although, I read many times that the plant has already done it and we will not have to do anything from us, but still. But first, pay attention to the upper left corner of the DSN-VC288 board, the two metallized holes are intended for mounting the device on zero.

So, if the device shows no current when idle, then:

- turn off the prefix;

- securely close the two contacts with tweezers;

- turn on the prefix;

- remove tweezers;

- turn off our the prefix from the power supply, and connect it again.

Load Testing

I don’t have a powerful resistor, but there was a piece of nichrome spiral: In the cold state, the resistance was about 15 ohms, in the hot, about 17 ohms. On the video,You can see the test of the resulting set-top box just for such a load, I compared the current with a sample device. The power supply was taken at 12 volts from a long-gone laptop. The video also shows the adjustable voltage range at the output of the device.

Total

- the device is not afraid of a short circuit;

- not afraid of overheating;

- not afraid of an open circuit of an adjusting resistor, if it breaks, the voltage automatically drops to a safe level below one and a half volts;

is a prefix, so it will easily survive if the input and output are interchanged when connected - this happened;

- there will be any external power supply from 7 volts to 30 volts maximum.